Method for cleaning the screen stencil of a silk-screen printing device and silk-screen printing machine for said method

ABSTRACT

The invention relates to a cleaning method for the screen stencil of a silk-screen printing machine. According to said method, prior to an intermediate printing process designed to clean the screen stencil, the underside of said stencil is wet with a cleaning agent that dissolves dye. The invention also relates to an intermediate printing device comprising an intermediate printing roll that can be displaced back and forth. A rotating roll that is immersed in a cleaning bath is situated at the front end of said intermediate printing roll. The rotating roll can be brought into contact with the underside of the screen stencil prior to the intermediate printing process by means of a pivoting device.

This application is a continuation of International applicationPCT/EP2003/011475, filed Oct. 16, 2003 and claims the priority of Germanapplication No. 102 56 326.8, filed Nov. 27, 2002, the disclosure ofwhich are expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a method for cleaning the screen stencil of ascreen printing device in which a sheet of paper is placed beneath thescreen stencil for an intermediate printing and is printed by a squeegeepassing over the stencil. This invention also relates to a screenprinting machine for performing this method.

A cleaning method and a screen printing machine suitable for performingthe cleaning method are known from DE 199 17 794 C2. With this knownmachine, the intermediate printing table is designed as a table that canbe pivoted parallel to the guide path of the printing table and which isbelow the guidance of the printing table during the printing process andis pivoted upward for the purpose of cleaning beneath the screen stencilfor the intermediate printing.

Machines of this type function satisfactorily but cannot prevent thedisadvantage that the screen printing ink may dry out in part and clogthe screen. Therefore despite the arrangement of an intermediateprinting table which is used for cleaning the screen, it is stillnecessary with screen printing devices to stop production to clean thescreen.

The object of the present invention is to perform such a cleaningoperation automatically for the most part and to perform it duringoperation to avoid production downtime. At the same time, better workingconditions are to be created and rejects are to be prevented.

To achieve this object, it is provided that before performing theintermediate printing, the bottom side of the screen stencil is wettedwith a cleaning agent. Due to this measure, even ink residues that havealready dried are dissolved from the screen; these residues could nothave been removed from the screen stencil through the measure of anintermediate printing, which is performed by moving the squeegeemechanism onto an intermediate printing paper which is then rolled upand removed.

In another embodiment of the inventive method, wetting is performed by arotating cylinder or brush which is brought into contact with the bottomside of the screen stencil and is immersed in a cleaning fluid. Due tothe rotation of the cylinder or brush, the cleaning agent is conveyedout of the bath and brought to the bottom side of the screen stencil,where it can loosen dried-on ink residues which can then be removed inthe intermediate printing.

This invention also relates to a screen printing machine for performingthe cleaning method, whereby the screen printing machine is equippedwith an intermediate printing device with which a sheet of paper can beintroduced beneath the screen stencil for the purpose of cleaning. Thenew screen printing machine is characterized by a rotating body assignedto the intermediate printing device and arranged across the direction ofmovement of the intermediate printing device, said rotating body beingcoatable with a cleaning agent and coming in contact with the bottomside of the screen stencil before the intermediate printing and beingguidable along the stencil.

Due to this design, the cleaning can be performed automatically and inthe screen printing machine.

In an embodiment of this invention, a cylinder which is immersed in abath of cleaning agent may be provided as the rotating body.

In a refinement of this invention, this cleaning agent may be present ina container that surrounds the bottom of the cylinder and is adapted tothe shape of the cylinder, in which case the cylinder is designed with aroughened surface to retain a sufficiently thick layer of cleaning agentand to be able to bring it against the screen stencil.

In a refinement of this invention, the cylinder is driven in a rotatingmanner and to this end engages in a toothed rod with pinion gearsarranged at the side next to the screen stencil on the printing machine.

The intermediate printing device itself is designed so that it can beraised and lowered and thus can be folded up and unfolded in which casea control device may be provided for determining the cleaning cycle sothat, for example, a cleaning printing operation is performed afterevery second, third or fourth printing.

In an advantageous refinement, the cylinder and the container assignedto it to which the cleaning agent is supplied in circulation in a simplemanner are arranged on the end of a paper impression cylinder mounteddisplaceably in the direction of movement of the squeegee, where saidend of the cylinder faces the screen stencil.

To implement the possibility of raising and lowering the cleaning agentcylinder, the cylinder together with the container may expediently bearranged on a pair of swivel levers that can be acted upon by pneumaticcylinders so that the lateral pinion gears of the cylinder engage in thetoothed rod which runs fixedly next to the screen stencil. Finally, inan essentially known manner, the intermediate impression cylinder may beprovided with paper and arranged so that it can be moved at least by thelength of the screen stencil, so that before the intermediate printingthe entire underside side of the screen stencil is wettable with acleaning agent. In practice, it is sufficient to wet the stencil in theprinting area.

Instead of the intermediate impression cylinder with an unrolling web ofpaper, an endless sheeting material may also be used to accommodate theintermediate printing or a plate cylinder may be used. In both variants,continuous cleaning of the continuous loop or the plate cylinder may beensured. Then there is no consumable material in the form of paper.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawingsfor example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic perspective diagram of an intermediate printingdevice according to an embodiment of this invention and its correlationwith the screen stencil of a screen printing machine, whose printingtable and squeegee mechanism are not shown,

FIG. 2 shows an enlarged diagram of the end of the intermediate printingdevice according to FIG. 1 facing the screen stencil but in a positionin which the intermediate printing device is in the process of being runbeneath the screen stencil to perform an intermediate printing, and

FIG. 3 shows a diagram like that in FIG. 1, as the underside of thescreen stencil is being wetted-with a cleaning agent.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an intermediate printing device 1 which is assigned to ascreen printing machine (not shown). Of the screen printing machine, thescreen stencil 2 which is held in a frame is shown here; it is arrangedin a known manner between an intermediate impression cylinder that canbe moved beneath it and a squeegee mechanism arranged above it (notshown). In addition, a toothed rod 3 which is arranged to run laterallyand parallel to the longitudinal direction of the screen stencil 2 andwill be discussed in greater detail below is fixedly connected to thescreen printing machine.

The intermediate printing device 1 is equipped with a paper web 5 withina carrying frame 4; this paper web is pulled off a cylinder and guidedover an intermediate impression cylinder 7 and back beneath it again toa second cylinder. The paper web 5 is guided here within the carryingframe 4 in such a way that it can also execute a back and forth movementof the intermediate impression cylinder 7 in the direction of arrows 8.

Upstream from the intermediate impression cylinder 7, a cylinder 9 isarranged running across the path of movement of the intermediateimpression cylinder 7; as indicated in the enlarged diagram in FIG. 2,this cylinder is immersed in a container 10 which largely surrounds itand is filled with a liquid cleaning agent. This is a cleaning agentcapable of dissolving the ink used in screen printing.

The container 10 and the cylinder 9 guided in it are mounted on atransverse web 11, which is mounted at the right end by a double lever13 pivotable about the axle 12. The other lever arm 13a of the doublelever is in contact with the tappet 14 of a pneumatic cylinder 15 whichmakes it possible to pivot the double lever 13 upward and downward outof the position illustrated in FIG. 1.

The cylinder 9 is provided with a pinion gear 16 on one end on which itis mounted via bearing journals, each in one end wall of the container10; on operation of the cylinder 15 and on pivoting of the double lever13 counterclockwise, this pinion gear engages with the toothed rod 3 asalso illustrated in FIG. 2.

The intermediate impression cylinder 7 protruding out of the carryingframe 4 has a bearing and two laterally protruding straps 17 which canbe brought into operative engagement with the squeegee mechanism (notshown) and/or with the drive thereof.

The operation of the intermediate printing device is as follows:

After a predetermined number of printing operations in the screenprinting machine, a pulse is delivered via a corresponding controldevice, resulting in the intermediate impression cylinder 7 being movedbeneath the screen stencil of the screen printing machine in the returnmotion of the squeegee mechanism, as illustrated in FIG. 3. Previously,the double lever 13 has been pivoted counterclockwise by cylinder 15 dueto the pulse, so that the cleaning agent cylinder 9 with its piniongears 16 engages with the toothed rod mounted fixedly next to the screenstencil 2. In the movement of the intermediate impression cylinder inthe direction of the arrow 18 (FIG. 3), the counterclockwise rotatingcylinder 9 is guided past the screen stencil 2, so that it comes incontact with the underside of the screen stencil 2. Therefore, as thecylinder 9 slides along the bottom side of the screen stencil 2, it wetsthe screen stencil 2 with a cleaning agent that is conveyed out of thecontainer 10 due to the rotation of the cylinder 9. The cleaning agentis also circulated through the container 10 in a manner not illustratedfurther here so that the level of the cleaning agent in the container 10can always be kept the same. Due to the wetting of the screen stencilwith the cleaning agent, ink residues are dissolved from the screenstencil, even if the ink is already partially dried. The cylinder 9 maybe passed once or more along the bottom side for wetting the bottom ofthe screen stencil so that the required wetting is accomplished in anycase. The intermediate impression cylinder 7 is to this end moved backand forth by the drive of the squeegee mechanism as often as necessary.

If the wetting is complete and has been continued long enough, then theintermediate impression cylinder 7 slides with the paper web 5completely under the screen stencil 2 and after lowering the squeegeemechanism, the remaining ink is printed out on the paper web 5 which isthen pulled off accordingly and rolled up as waste. Dried-on inkresidues are also removed from the screen stencil 2 in this cleaning.

Then the normal printing operation is again begun. Through appropriatecontrol, it is possible after a certain number of printings to perform acleaning again, whereby after a predetermined number of printings, thewetting of the bottom side of the screen stencil can also beaccomplished automatically by passing the cylinder 9 once along thescreen stencil or even repeated many times back and forth along thebottom of the screen stencil 2.

Once the wetting operation of the bottom side of the screen stencil isconcluded, the pinion gear 16 is removed from the toothed rack 3 bypivoting the double lever 13 clockwise so that the screen stencil 2 isno longer being wetted for the cleaning printing itself and for thecorresponding return movement of the intermediate impression cylinder 7.

This invention offers a very simple possibility of cleaning a screenstencil 2 of a screen printing machine which takes place automatically.The device is largely maintenance-free and allows cleaning of the screenwithout any mentionable production downtime.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1-18. (canceled)
 19. Method for cleaning the screen stencil of a screenprinting device, wherein a paper web is brought beneath the screenstencil for an intermediate printing and is printed by a squeegeerunning over it, wherein before performing the intermediate printing,the bottom of the screen stencil is wetted with a cleaning agent. 20.Method as claimed in claim 19, wherein the wetting is performed by arotating cylinder or brush that is immersed in cleaning agent andbrought in contact with the bottom of the screen stencil. 21.Intermediate printing device for a screen printing machine for cleaninga screen stencil, having a paper web and an intermediate impressioncylinder which can be inserted beneath the screen stencil for thepurpose of cleaning the screen stencil, wherein a rotating body which isprovided for the intermediate printing device and is mounted across adirection of movement of the intermediate printing device, said rotatingbody being coatable with a cleaning agent and guidable along and incontact with a bottom of the screen stencil before an intermediateprinting.
 22. Intermediate printing device as claimed in claim 21,wherein the rotating body is a cylinder which is immersed in a cleaningagent bath.
 23. Intermediate printing device as claimed in claim 22,wherein the cleaning agent is accommodated in a container whichsurrounds at least a bottom portion of the cylinder and is adapted tothe shape of the cylinder.
 24. Intermediate printing device as claimedin claim 23, wherein the cleaning agent is supplied to the container incirculation.
 25. Intermediate printing device as claimed in claim 22,wherein the surface of the cylinder is roughened.
 26. Intermediateprinting device as claimed in claim 22, wherein the cylinder is providedwith a pinion gear arranged laterally and engaging in a toothed rodwhich is fixedly arranged on the master frame of the screen printingmachine next to the screen stencil.
 27. Intermediate printing device asclaimed in claim 21, wherein the rotating body is designed so that itcan be raised and lowered.
 28. Intermediate printing device as claimedin claim 21, wherein a control device is provided for determining thecleaning cycle.
 29. Intermediate printing device as claimed in claim 22,wherein the cylinder and the container assigned to it for the cleaningagent are arranged on the end of an intermediate impression cylinderwhich faces the screen stencil, said cylinder being mounted displaceablyin a direction of movement of the squeegee.
 30. Intermediate printingdevice as claimed in claim 29, wherein the cylinder is mounted with thecontainer on a pivot lever pair.
 31. Intermediate printing device asclaimed in claim 26, wherein the pivot lever pair can be acted upon bypneumatic cylinders so that the pinion gear engages in the toothed rod.32. Intermediate printing device as claimed in claim 21, wherein theintermediate impression cylinder is provided with a paper web carried bycylinders and arranged so that it can be displaced about the length ofthe screen stencil.
 33. Intermediate printing device as claimed in claim32, wherein the paper web is designed as a continuous loop to receiveink and cleaning agent.
 34. Intermediate printing device as claimed inclaim 33, wherein the continuous loop material is freed of ink withcleaning agent in circulation and is available again for reprinting whendry.
 35. Intermediate printing device as claimed in claim 34, whereinthe cleaning of the continuous loop material is accomplished withcleaning agent that is carried in circulation and using brushes,stripping squeegees and spray nozzles.
 36. Intermediate printing deviceas claimed in claim 21, wherein the intermediate printing is performedfor cleaning the screen stencil with a plate cylinder rolling beneaththe screen, and the intermediate printing for cleaning is performedautomatically.